Cryptomatte aliased/jagged edges output
The colored image as shown in the question is the output from the picker image of the cryptomatte node. This image is used to quickly pick an object or material from the cryptomatte data. It is not the actual matte.
After picking objects and materials the anti aliased mask will be available from the matte output of the cryptomatte node. This is answered in more detail in Cryptomatte - Clean edges